1. Field of the Invention
The present invention relates to a connector used in a portable radio terminal such as a mobile telephone and a small-sized electronic device such as a laptop PC, or the like. In more detail, the present invention relates to a multipolar connector in which a plurality of contacts are assembled at prescribed spacings in a longitudinal direction of a laterally long body, and a portable radio terminal or a small-sized electronic device using such multipolar connector.
2. Description of the Related Art
In a mobile telephone or a laptop PC, a connector of a multipolar circuit board mounting type is used to connect cables connected to a liquid crystal display device or the like to a circuit board on a motherboard. A connector of this type is composed of a laterally long connector plug in which a plurality of cables are assembled, and a laterally long receptacle of a circuit board mounting type to which the connector plug is fitted, as described, for example, Japanese Laid-Open Patent Application No. 2000-331731, Japanese Laid-Open Patent Application No. 2005-71669 and Japanese Laid-Open Patent Application No. 2005-116447.
Generally, a laterally long connector plug is formed in a cap-type which covers a laterally long receptacle, and has a number of plug contacts aligned at prescribed spacings in a longitudinal direction (lateral width direction). The plug contacts are electrically connected to a number of cables assembled. On the other hand, the receptacle has a number of receptacle contacts aligned at prescribed spacings in a longitudinal direction (lateral width direction) so as to correspond to the plug contacts. The receptacle contacts are inserted in slit-shaped insertion parts that are arranged orthogonally to the longitudinal direction and formed at prescribed spacings in a longitudinal direction of a laterally long plastics material body. One end part of each receptacle contact is a contact part which press-contacts the corresponding plug contact. The other end part is a circuit board mounting part, which is to be joined to the wiring pattern formed on the surface of a circuit board by soldering or the like.
Generally, in order to secure elastic contact with the plug contact, a meandering curved part as an elastic deformation part is provided between the contact part and the circuit board mounting part.
By attaching the connector plug to the receptacle mounted on the surface of the circuit board, respective meandering curved parts and the like of the receptacle contacts in the receptacle elastically deform, and with the repulsions thereof, the receptacle contacts press-contact the corresponding plug contacts in the connector plug. Thereby, the cables assembled to the connector plug are electrically connected to the wiring pattern formed on the surface of the circuit board.
In such a connector of the multipolar circuit board mounting type, the both end parts of the receptacle body, that is, the both sides of the receptacle contact group are provided with ground terminals also serving as mounting terminals for securing joining strength with the circuit board of the receptacle and shielding and the like. However, since a number of receptacle contacts are arranged between the ground terminals on the both ends, distances from contacts to ground terminals differ depending on the arranged positions of the receptacle contacts. That is, contacts arranged toward opposite ends of the body are closer to the ground terminal, and for contacts positioned closer to the center part while separated from the ends, distances to the ground terminal increase. As a result, impedance characteristics differ between contacts, causing the following problems.
For performing high-speed digital signal processing, impedance characteristics must be consistent in the connector passing area. In performing differential transmission, as the skew (difference in electric lengths) between two lines increases, transmission characteristics of differential transmission paths decline. Further, in the case of transmitting electric signals through a plurality of differential lines, if the skew increases between differential pairs, there is a risk that more errors may be caused in the processing on the reception side. In the case of the conventional structure described above, a difference in impedance characteristics is caused between contacts, so the skew becomes larger, whereby the skew between the differential pairs also becomes larger. Consequently, problems such as decline in transmission characteristics and an increase in errors on the reception side are caused.
In order to solve these problems, a conventional solution is to use contacts on the opposite ends of differential pairs in opposite poles as ground terminals so as to secure consistency in impedance characteristics between the opposite poles. However, the required number of contacts increases, so not only the number of components increases, but also the connector becomes enlarged in a longitudinal direction (contact aligning direction).
In addition, in high-speed digital signal processing, circuit board wiring, cable wiring and connector wiring are not mere connection lines, but they must be considered as signal transmission paths, so it is required to give consideration to making the positional relationship between the signal transmission paths and the ground constant. Namely, not only in a contact alignment direction but also in a direction orthogonal to the contact alignment direction, it is necessary to keep the positional relationships between the contacts and the ground constant, and to uniform the impedance characteristics.
However, in the conventional receptacle of a circuit board mounting type, in order to secure elastic contact with a corresponding contact on the plug side, a meandering curved part is often provided in the intermediate portion of the receptacle contact, as described above. Consequently, the positional relationship with the ground largely changes in the meandering curved part. This also causes a problem due to inconsistency in the impedance characteristics.